Methods for the electronic, homogeneous assembly and fabrication of devices

ABSTRACT

Methods are provided for the fabrication of microscale, including micron and sub-micron scale, including nanoscale, devices. Electronic transport of movable component devices is utilized through a fluidic medium to effect transport to a desired target location on a substrate or motherboard. Forces include electrophoretic force, electroosmotic force, electrostatic force and/or dielectrophoretic force. In the preferred embodiment, free field electroosmotic forces are utilized either alone, or in conjunction with, other forces. These forces may be used singly or in combination, as well as in conjunction with yet other forces, such as fluidic forces, mechanical forces or thermal convective forces. Transport may be effected through the use of driving electrodes so as to transport the component device to yet other connection electrodes. In certain embodiments, the component devices may be attached to the target device using a solder reflow step.

RELATED APPLICATION INFORMATION

This application is a continuation application of application Ser. No.10/337,450, filed Jan. 6, 2003, entitled “Methods for the Electronic,Homogenous Assembly and Fabrication of Devices,” now allowed, which is acontinuation application of application Ser. No. 09/436,311, filed Nov.8, 1999, entitled “Methods for the Electronic, Homogenous Assembly andFabrication of Devices,” now allowed, which is a continuation-in-partapplication of application Ser. No. 08/760,933, filed Dec. 6, 1996,entitled “Affinity Based Self-Assembly Systems and Devices for Photonicand Electronic Applications”, which is a continuation-in-partapplication of application Ser. No. 08/534,454, filed Sep. 27, 1995,entitled “Apparatus and Methods for Active Programmable Matrix Devices”,now issued as U.S. Pat. No. 5,849,486, which is a continuation-in-partof application Ser. No. 08/304,657, filed Sep. 9, 1994, entitled, asamended, “Molecular Biological Diagnostic Systems Including Electrodes”,now issued as U.S. Pat. No. 5,632,957, which is a continuation-in-partof application Ser. No. 08/271,882, filed Jul. 7, 1994, entitled, asamended, “Methods for Electronic Stringency Control for MolecularBiological Analysis and Diagnostics”, now allowed, which is acontinuation-in-part of application Ser. No. 08/146,504, filed Nov. 1,1993, entitled, as amended, “Active Programmable Electronic Devices forMolecular Biological Analysis and Diagnostics”, now issued as U.S. Pat.No. 5,605,662, application Ser. No. 08/703,601, filed Aug. 23, 1996,entitled “Hybridization of Polynucleotide Conjugated with Chromophoresand Fluorophores to Generate Donor-to-Donor Energy Transfer System”, nowallowed, which is a continuation of application Ser. No. 08/232,233,filed May 5, 1994, entitled “Hybridization of Polynucleotide Conjugatedwith Chromophores and Fluorophores to Generate Donor-to-Donor EnergyTransfer System”, now issued as U.S. Pat. No. 5,565,322, which is acontinuation-in-part of application Ser. No. 07/790,262, filed Nov. 7,1991, entitled “Self-Organizing Molecular Photonic Structures Based onChromophore- and Fluorophore-Containing Polynucleotide and Methods ofTheir Use”, now issued as U.S. Pat. No. 5,532,129 (via continuationapplication Ser. No. 08/250,951, filed May 27, 1994), application Ser.No. 09/129,470, entitled “DNA Optical Storage Memory”, filed Aug. 5,1998, pending, which is a continuation of application Ser. No.08/906,569, entitled “Optical Storage Device Utilizing Non-RadiativeEnergy Transfer” now issued as U.S. Pat. No. 5,835,404, which is acontinuation of application Ser. No. 08/258,168, filed Jun. 10, 1994,entitled “DNA Optical Storage”, now issued as U.S. Pat. No. 5,787,032,and application Ser. No. 08/968,065, entitled “Methods and Proceduresfor Molecular Biological Analysis and Diagnostics”, filed Dec. 5, 1997,now pending, which is a continuation-in-part of application Ser. No.08/855,058, entitled “Methods for Electronic Perturbation Analysis ofBiological Materials”, filed May 14, 1997, pending, all incorporatedherein by reference as if fully set forth herein.

FEDERAL FUNDS STATEMENT

This invention was made with Government support under ContractF30602-97-C-0155 awarded by the Air Force. The Government has certainrights in this invention.

FIELD OF THE INVENTION

This invention relates to methodologies and techniques for the design,fabrication and use of a fluidic system incorporating means by whichelectric fields are applied to carry out the assembly of micron tonanoscale materials. By way of example, the inventions serve to formmicroelectronic, micromechanical, microoptical and mixed functiondevices or assemblies both in two dimensions and three dimensions. Thisinvention also relates to associated microelectronic and optoelectronicdevices, systems, and manufacturing platforms which provide electricfield transport, and optionally, selective addressing of components,including self-assembling, nanostructures, sub-micron and micron sizedcomponents to selected locations on the device itself or onto othersubstrate materials.

BACKGROUND OF THE INVENTION

The fields of molecular electronics/photonics and nanotechnology offerimmense technological promise for the future. Nanotechnology is definedas a projected technology based on a generalized ability to buildobjects to complex atomic specifications. Drexler, Proc. Natl. Acad. SciUSA, 78:5275-5278, (1981). Nanotechnology generally means anatom-by-atom or molecule-by-molecule control for organizing and buildingcomplex structures all the way to the macroscopic level. Nanotechnologyis a bottom-up approach, in contrast to a top-down strategy like presentlithographic techniques used in the semiconductor and integrated circuitindustries. The success of nanotechnology may be based on thedevelopment of programmable self-assembling molecular units andmolecular level machine tools, so-called assemblers, which will enablethe construction of a wide range of molecular structures and devices.Drexler, “Engines of Creation,” Doubleday Publishing Co., New York, N.Y.(1986).

Present molecular electronic/photonic technology includes numerousefforts from diverse fields of scientists and engineers. Carter, ed.,“Molecular Electronic Devices II,” Marcel Dekker, Inc, New York, N.Y.(1987). Those fields include organic polymer based rectifiers, Metzgeret al., “Molecular Electronic Devices II,” Carter, ed., Marcel Dekker,New York, N.Y., pp. 5-25 (1987), conducting conjugated polymers,MacDiarmid et al., Synthetic Metals, 18:285 (1987), electronicproperties of organic thin films or Langmuir-Blogett films, Watanabe etal., Synthetic Metals, 28:C473 (1989), molecular shift registers basedon electron transfer, Hopfield et al., Science, 241:817 (1988), and aself-assembly system based on synthetically modified lipids which form avariety of different “tubular” microstructures. Singh et al., “AppliedBioactive Polymeric Materials,” Plenum Press, New York, N.Y., pp.239-249 (1988). Molecular optical or photonic devices based onconjugated organic polymers, Baker et al., Synthetic Metals, 28:D639(1989), and nonlinear organic materials have also been described.Potember et al., Proc. Annual Conf. IEEE in Medicine and Biology, Part4/6:1302-1303 (1989).

However, none of the cited references describe a sophisticated orprogrammable level of manufacturing self-organization or self-assembly.Typically, the actual molecular component which carries out theelectronic and/or photonic mechanism is a natural biological protein orother molecule. Akaike et al., Proc. Annual Conf. IEEE in Medicine andBiology, Part 4/6:1337-1338 (1989). There are presently no examples of atotally synthetic programmable self-assembling molecule which producesan efficient electronic or photonic structure, mechanism or device.

Progress in understanding self-assembly in biological systems isrelevant to nanotechnology. Drexler, Proc. Natl. Acad. Sci USA,78:5275-5278 (1981), and Drexler, “Engines of Creation,” DoubledayPublishing Co., New York, N.Y. (1986). Areas of significant progressinclude the organization of the light harvesting photosynthetic systems,the energy transducing electron transport systems, the visual process,nerve conduction and the structure and function of the proteincomponents which make up these systems. The so-called bio-chipsdescribed the use of synthetically or biologically modified proteins toconstruct molecular electronic devices. Haddon et al., Proc. Natl. Acad.Sci. USA, 82:1874-1878 (1985), McAlear et al., “Molecular ElectronicDevices II,” Carter ed., Marcel Dekker, Inc., New York N.Y., pp. 623-633(1987).

Some work on synthetic proteins (polypeptides) has been carried out withthe objective of developing conducting networks. McAlear et al.,“Molecular Electronic Devices,” Carter ed., Marcel Dekker, New York,N.Y., pp. 175-180 (1982). Other workers have speculated that nucleicacid based bio-chips may be more promising. Robinson et al., “The Designof a Biochip: a Self-Assembling Molecular-Scale Memory Device,” ProteinEngineering, 1:295-300 (1987).

Great strides have also been made in the understanding of the structureand function of the nucleic acids, deoxyribonucleic acid or DNA, Watson,et al., in “Molecular Biology of the Gene,” Vol. 1, Benjamin PublishingCo., Menlo Park, Calif. (1987), which is the carrier of geneticinformation in all living organisms (See FIG. 1). In DNA, information isencoded in the linear sequence of nucleotides by their base unitsadenine, guanine, cytosine, and thymidine (A, G, C, and T). Singlestrands of DNA (or polynucleotide) have the unique property ofrecognizing and binding, by hybridization, to their complementarysequence to form a double stranded nucleic acid duplex structure. Thisis possible because of the inherent base-pairing properties of thenucleic acids: A recognizes T, and G recognizes C. This property leadsto a very high degree of specificity since any given polynucleotidesequence will hybridize only to its exact complementary sequence.

In addition to the molecular biology of nucleic acids, great progresshas also been made in the area of the chemical synthesis of nucleicacids. This technology has developed so automated instruments can nowefficiently synthesize sequences over 100 nucleotides in length, atsynthesis rates of 15 nucleotides per hour. Also, many techniques havebeen developed for the modification of nucleic acids with functionalgroups, including: fluorophores, chromophores, affinity labels, metalchelates, chemically reactive groups and enzymes. Smith et al., Nature,321:674-679 (1986); Agarawal et al., Nucleic Acids Research,14:6227-6245 (1986); Chu et al., Nucleic Acids Research, 16:3671-3691(1988).

An impetus for developing both the synthesis and modification of nucleicacids has been the potential for their use in clinical diagnosticassays, an area also referred to as DNA probe diagnostics. Simplephotonic mechanisms have been incorporated into modifiedoligonucleotides in an effort to impart sensitive fluorescent detectionproperties into the DNA probe diagnostic assay systems. This approachinvolved fluorophore and chemilluminescent-labeled oligonucleotideswhich carry out Förster nonradiative energy transfer. Heller et al.,“Rapid Detection and Identification of Infectious Agents,” Kingsbury etal., eds., Academic Press, New York, N.Y. pp. 345-356 (1985). Försternonradiative energy transfer is a process by which a fluorescent donorgroup excited at one wavelength transfers its absorbed energy by aresonant dipole coupling process to a suitable fluorescent acceptorgroup. The efficiency of energy transfer between a suitable donor andacceptor group has a 1/r⁶ distance dependency (see Lakowicz et al.,“Principles of Fluorescent Spectroscopy,” Plenum Press, New York, N.Y.,Chap. 10, pp. 305-337 (1983)).

As to photonic devices, they can generally be fabricated in dense arraysusing well developed micro-fabrication techniques. However, they canonly be integrated over small areas limited by the relatively highdefect densities of the substrates employed. In order to be useful andeconomically viable, these devices must in many cases, be used withinlarge area silicon integrated circuits. A good example of this issue isthe vertical cavity surface emitting lasers. To address many potentialapplications, it would be highly desirable to integrate these deviceswith large area silicon IC's. A major obstacle in the integration ofthese new devices with silicon is the existence of material andgeometrical incompatibilities. These devices need to be integrated onsilicon in large sparse arrays with minimal performance degradation, andwithout affecting the underlying silicon circuits. Over the past years,a number of component assembly technologies have been extensivelyinvestigated regarding the integration of such compound semiconductordevices on silicon. These include hybrid flip-chip bonding or epitaxiallift-off and other direct bonding methods. Although these hybridtechnologies have made significant progress and several componentdemonstrations have shown the viability of these techniques, thesemethods do not address the problem of geometrical incompatibility. Thatis, the dimensions with which the specialty devices are fabricated ontheir mother substrate must be conserved when they are coupled onto thehost substrate. This makes the integration of small area devices onlarge area components economically unfeasible.

A major obstacle in the integration of these new devices with silicon isthe existence of material and geometrical incompatibilities. Thesedevices need to be integrated on silicon in large sparse arrays withminimal performance degradation, and without affecting the underlyingsilicon circuits. Over the past years, a number of component assemblytechnologies have been extensively investigated regarding theintegration of such compound semiconductor devices on silicon. Theseinclude hybrid flip-chip bonding or epitaxial lift-off and other directbonding methods. Although these hybrid technologies have madesignificant progress and several component demonstrations have shown theviability of these techniques, these methods do not address the problemof geometrical incompatibility. That is, the dimensions with which thespecialty devices are fabricated on their mother substrate must beconserved when they are coupled or grafted onto the silicon board.

Efforts have been made to fabricate self-assembling microstructures ontoa substrate through fluid transport. For example, in U.S. Pat. No.5,783,856, entitled “Method for Fabricating Self-AssemblingMicrostructures”, methods and apparatus are disclosed which utilizedmicrostructures having shaped blocks which self-align into recessedregions located on a substrate such that the microstructure becomesintegral with the substrate. A slurry containing multiple devices isthen poured over the substrate bearing the recessed regions such thatthe microstructures selectively engage with the substrate.

The prior art has no integration technique that is capable of creating asparse array of devices distributed over a large area, when the devicesare originally fabricated densely over small areas. This makes largearea components made up from integration of micron size deviceseconomically unfeasible. To solve this problem, the electronics industryemploys a hierarchy of packaging techniques. However, this problemremains unsolved when a regular array of devices is needed on largeareas with a relatively small pitch. This problem is probably mostnoticeable through the high cost associated with the implementation ofmatrix addressed displays, where the silicon active matrix consists ofsmall transistors that need to be distributed over a large area. Thus,prior art microfabrication techniques limit devices to small areacomponents where a dense array of devices are integrated. However, thereare a number of important applications that could benefit from specialtydevices being integrated more sparsely over large areas.

One possible method for removing the geometrical limitations is thefurther development of semiconductor substrate materials to the pointwhere their defect densities approaches that of silicon. This is a longand expensive process that requires incremental progress. A secondapproach is the development of special robots capable of handling micronand sub-micron size devices and able to graft them to appropriateplaces. This also seems impractical because the grafting process willremain sequential where one device may be grafted after another,requiring impractical processing times. In any case, both of theseapproaches may be limited to motherboard dimensions on the order of 10cm.

With regard to memories, data processing engines have been physicallyand conceptually separated from the memory which stores the data andprogram commands. As processor speed has increased over time, there hasbeen a continuous press for larger memories and faster access. Recentadvances in processor speed have caused system bottlenecks in access tomemory. This restriction is critical because delays in obtaininginstructions or data may cause significant processor wait time,resulting in loss of valuable processing time.

Various approaches have been taken to solve these concerns. Generally,the solutions include using various types of memory which have differentattributes. For example, it is common to use a relatively small amountof fast, and typically expensive, memory directly associated with theprocessor units, typically called cache memory. Additionally, largercapacity, but generally slower, memory such as DRAM or SRAM isassociated with the CPU. This intermediate memory is often large enoughfor a small number of current applications, but not large enough to holdall system programs and data. Mass storage memory, which is ordinaryvery large, but relatively inexpensive, is relatively slow. Whileadvances have been continually made in improving the size and speed ofall types of memory, and generally reducing the cost per bit of memory,there remains a substantial need especially to serve yet fasterprocessors.

For the last 20 years most mass storage devices have utilized a rotatingmemory medium. Magnetic media have been used for both “floppy”(flexible) disks or “hard” disk drives. Information is stored by thepresence or absence of magnetization at defined physical locations onthe disk. Ordinarily, magnetic media are “read-write” memories in thatthe memory may be both written to and read from by the system. Data iswritten to or read from the disk by heads placed close to the surface ofthe disk.

A more recent development in rotating mass storage media are the opticalmedia. Compact disks are read only memory in which the presence orabsence of physical deformations in the disk indicates the data. Theinformation is read by use of a focused laser beam, in which the changein reflectance properties from the disk indicate the data states. Alsoin the optical realm are various optical memories which utilizemagnetooptic properties in the writing and reading of data. These disksare both read only, write once read many (“WORM”) drives and multipleread-write memories. Generally, optical media have proved to have alarger storage capacity, but higher costs per bit and limited writeability, as compared with magnetic media.

Several proposals have been made for using polymers for electronic basedmolecular memories. For example, Hopfield, J. J., Onuchic, J. N. andBeratan, D. N., “A Molecular Shift Register”, Science, 241, p. 817,1988, discloses a polymer based shift register memory which incorporatescharge transfer groups. Other workers have proposed an electronic basedDNA memory (see Robinson et al, “The Design of a Biochip: ASelf-Assembling Molecular-Scale Memory Device”, Protein Engineering,1:295-300 (1987)). In this case, DNA is used with electron conductingpolymers for a molecular memory device. Both concepts for thesemolecular electronic memories do not provide a viable mechanism forinputting data (write) and for outputting data (read).

Molecular electronic memories have been particularly disappointing intheir practical results. While proposals have been made, and minimalexistence proofs performed, generally these systems have not beenconverted to commercial reality. Further, a specific deficiency of thesystem described above is that a sequential memory is typicallysubstantially slower than a random access memory for use in mostsystems.

The optical memories described above suffer from the particular problemof requiring use of optical systems which are diffraction limited. Thisimposes size restrictions upon the minimum size of a data bit, therebylimiting memory density. This is an inherent limit in systems whichstore a single bit of data at a given physical memory location.

Further, in all optical memory systems described above, the informationis stored on a bit-by-bit basis, such that only a single bit of data isobtained by accessing a giving physical location in memory. Whileword-wide memory access systems do exist, generally they store but asingle bit of information at a given location, thereby requiringsubstantially the same amount of physical memory space whether accessedin a bit manner or word-wide manner.

While systems have generally increased in speed and storage density, anddecreased in cost per bit, there remains a clear gap at present betweenprocessor speed and system requirements. See generally, “New MemoryArchitectures to Boost Performance”, Tom R. Halfhill, Byte, July, 1993,pp. 86 and 87. Despite the general desirability of memories which arefaster, denser and cheaper per bit, and the specific critical need formass memory which can meet the demands of modern day processor systemsspeed, no completely satisfactory solution has been advanced heretofore.The fundamental limitations on the currently existing paradigms cannotbe overcome by evolutionary enhancements in those systems.

Despite the clear desirability for new and improved apparatus andmethods in this field, no optimal solution has been proposed previously.

SUMMARY OF THE INVENTION

Increasingly, the technologies of communication, information processing,and data storage are beginning to depend upon highly-integrated arraysof small, fast electronic and photonic devices. As device sizes scaledown and array sizes increase, conventional integration techniquesbecome increasingly costly. The dimensions of photonic and electronicdevices permit the use of electronic assembly and/or molecularbiological engineering for the integration and manufacturing of photonicand electronic array components. This invention also relates toassociated microelectronic and optoelectronic devices, systems, andmanufacturing platforms which provide electric field transport andselective addressing of self-assembling, nanostructures, sub-micron andmicron size components to selected locations on the device itself oronto other substrate materials.

More broadly, the invention in this respect relates to a method for thefabrication of micro scale and nanoscale devices comprising the steps offabricating first component devices on a first support, releasing atleast one first component device from the first support, transportingthe first component device to a second support, and attaching the firstcomponent device to the second support. In particular, electrostatic,electrophoretic and electroosmotic forces may be employed to transport,position and orient components upon a suitably designed substrate eitherin sequential steps or in parallel. Optionally, nucleic acidhybridization or other forms of molecular biological or other forms ofreversibly binding systems may be employed to promote self-assembly andself-sorting of materials as components within or between components ofthese assemblies. A further aspect of this invention involves carryingout the various electric filed assisted assembly processed under lowgravity conditions, which may improved the overall performance.

This invention relates to the means of enabling micron and nanoscaleassembly in a fluid medium by use of electric fields for placement ofcomponents and subassemblies. This invention also encompasses thedesign, composition and manufacture of components, assembly substratesor platforms and component delivery systems as well as the compositionof the fluid medium. This technology lends itself to scaling dimensionsranging from the molecular (sub-nanometer) to the micron. Furthermore,the use of self-organizing or self-assembling molecules such aspolynucleic acids can serve to augment the overall utility of thisapproach. This broad flexibility is unique to this technology andrepresents a novel application of electric fields, devices andmaterials. The heterogeneous assembly of microelectronic, microopticaland micromechanical components upon an integrated silicon circuitrepresents one such use of this approach. Thus, this invention relatesto the employment of electric fields, the nature and scale of materialsto be assembled, the electrical and chemical properties of the assemblysurface or environment, the means by which electrical interconnects maybe formed and the potential utility of such assembled devices.

The electric fields relating to this invention can be eitherelectrostatic, electrophoretic, electroosmotic, or dielectrophoretic innature. In addition, the resultant forces used for component positioningmay be comprised of various combinations of these. In application, afluid medium, typically aqueous in composition, would be deposited ontothe assembly surface. This surface has one or more microlocations whichgovern the application of these electric fields through the fluidmedium. Devices or components for assembly are added to the fluid mediumand then are targeted by control of the electric fields to definedpositions upon the assembly surface. Transport is accomplished byinteractions between the device and the nature and effects of the forcesengendered by the electric fields. In particular, if net charges arepresent upon the components or devices, electrophoretic or possiblyelectrostatic forces would be factors governing movement of thematerials. Alternatively, if no net charge is present upon thesematerials, forces such as electroosmosis which enables bulk fluidmovement or dielectrophoresis may be employed to maneuver and locate thedevices at specific locations upon the surface. In certaincircumstances, both electrophoretic and electroosmotic (or othercombinations of forces) may work in combination to guide position andorientation of component assembly.

The use of electric fields has been described for the movement ofbiological molecules, typically nucleic acids or proteins, for thepurpose of analysis, diagnosis or separation. See, e.g., U.S. Pat. No.5,605,662. These inventions are more particularly directed to theassembly of micron to sub-micron to nano-scale assembly of components toform functional composite devices or sub-assemblies. Such heterogeneousintegration using these fields represents a novel means by whichassembly technology can progress to new dimensions and materials. Oneadvantage of this non-mechanical “pick-and-place” assembly technology isthe ability to handle a variety of component shapes and sizes upon acommon platform. In addition, the forces employed are self-governing inso far as the movement of the components is regulated by the componentsthemselves, i.e. their shape, their dimensions and their surface chargeand not dependent upon an external mechanical device. This featurethereby lessens or minimizes the likelihood of possible mechanicaldamage to possibly fragile components during placement.

Key to the utilization of this technology is an appropriately designedand composed assembly platform. Such a platform contains electrodes onthe assembly surface enabling the formation of electric fields thatestablish the forces necessary for transport of devices and componentsduring the assembly process. These electrodes may either be at the pointto which the components are to be located or adjacent to these locations(i.e. “drive” electrodes). The latter form of electrodes would typicallynot serve as electrical connection points to the assembly, but rather asaids to the assembly process. Other electrodes may serve both roles,operating both as driving points for assembly and as locations forelectrical contact between the components and the underlying assemblyplatform. Combinations of both drive electrodes and “contact” electrodesmay be present at any one assembly location or throughout the assemblyplatform.

Also, the surface of the assembly platform may be adopted or modifiedthrough lithographic techniques to present stop points or recesses intowhich the components can be electronically positioned. These arrestingpoints by themselves are constructed such that, in the absence ofapplied electronic control, movement of devices and components as wellas their orientation at these positions would not be possible.

The composition of the assembly surface is also modifiable in order tomore precisely match the needs of the assembly process. In particular,the surface can be covered with a permeable layer composed of hydrogels,SiO₂, or other related materials suitable for providing sites ofattachment for molecules useful for anchoring devices, components,nanoscale and molecular scale materials as well as serving as a means ofdistancing the assembly site from the reactive zone set up whenelectrolysis of water occurs.

The other form of coating would be one which modifies the inherentcharge of the surface and velocity of fluid, either augmenting,neutralizing or reversing electroosmotic flow along this surface. Incontrast to the permeation layer whose functionality and role is usefulat or adjacent to working electrodes, this surface modifying coat wouldbe functioning not at the active electrodes per se but at the assemblysurface between electrode locations.

A new class of components or devices would be designed for use with thissystem. That is, these components would contain features both enablingderivatization with suitable chemistry in order to provide charge and/orsites of attachment for molecules providing charge and/or self-assemblyfunctionality, e.g. nucleic acids, and would be constructed in such afashion as to provide contact features enabling electric connectionbetween the component and either the underlying assembly platform orother devices or materials attached to this component itself. Contactscould be so constructed as to remove the need for specific orientationof the device on the assembly platform. That is, by use of concentricring electrodes on the component device, the need to orient the deviceupon the assembly platform is removed by having an infinite number oforientations while in that plane being suitable. Alternatively, theoutside faces of the component or device might be shaped such as toenable locating into modified assembly surface features, e.g., use ofmatching shaped devices with corresponding surface depressions or stops.Such designs would serve to provide alignment of electrical andmechanical contacts for the devices and components to the assemblyplatform and to other components, devices, and sub-assemblies.

An important feature would the mechanism to deliver components andmaterials to the assembly platform. A microfluidic delivery headcomprised of both the means to contain components prior to applicationto the working platform and the counter electrode necessary to set theappropriate electric field geometry aiding assembly is one such designthat may be employed. Each of these two aspects represents novelapplication (and modification) of existing technology, e.g.microfluidics and electrode design. In addition, the means of fluidicdelivery itself may be combined with the counter electrode such thatdevices are either electrophoretically or electroosmotically transportedthrough the device head into fluid overlaying the assembly platform. Inan alternative embodiment, a device platform may receive a motherboardand provide the return electrode or conduction path for electrode siteson the motherboard. In this way, the number of electrodes on themotherboard may be reduced, and the device simplified. The deviceplatform may contain sources of component devices, such as substratesfrom which component devices are subject to lift-off.

Electrical or mechanical connections between assembled components maytake place either serially, as each set of components is arranged or asa final step in the assembly process. These connections depend in partupon the surfaces to be joined and the type of joint to be formed. Inparticular, we have discovered that metals can be electrodepositedthrough permeation layers to form electrical contact to materialspositioned at these locations. In addition, conductive materials, e.g.organic polymers, could be used to coat the polynucleotide scaffoldingemployed for self-assembly.

Some potential applications for these techniques are: (1) fabricatinglight emitter arrays over large surfaces; (2) assembly of two orthree-dimensional photonic crystal structures; (3) two and threedimensional high density data storage materials, devices and systems;and (4) manufacturing of various hybrid-integrated components includingflat panel displays, wireless/RF integrated devices, lab on a chipdevices, microcantiliver sensor devices, atomic force microscopedevices, integrated MEMS/optical/microelectronic devices, integratedmicroscopic analytical and diagnostic devices, and compact/handheldmedical diagnostic devices and systems.

As photonics plays an increasingly important role in informationprocessing, communication and storage systems it will deliver faster,smaller, more power efficient, and functionally versatile integratedsystems at lower cost. New fabrication technologies includingnanostructure fabrication, integration and self-assembly techniques areused. As device dimensions shrink to submicron levels, it becomesimportant to utilize the inventive concepts employing molecularbiological engineering concepts and principles as manufacturingtechniques for the fabrication of integrated photonic and electronicdevices.

In one particular implementation, light emitting diodes (LEDs) may befabricated on a support and removed therefrom utilizing a lift-offtechnique. Component devices such as the LEDs may then be placed on themotherboard or target device generally in the target position throughuse of electroosmotic force. Once the component device has beenappropriately placed, substantially permanent electrical contact withthe motherboard or target device is then effected. In the preferredembodiment, the component device is subject to a soldering technique,such as through a solder reflow technique.

In yet another aspect of this invention, methods for the assembly ofdevices in a low gravity environment are provided. More particularly,electrical transport, preferably electrostatic or electrophoretic, butalso possibly electroosmotic or dielectrophoretic, may be utilized in alow gravity environment to place devices from a source of devices ontotarget structures or motherboards and to then affixed and activate thosedevices on that target device or motherboard.

Accordingly, it is one object of this invention to enable micron andsub-micron (including nanotechnology) through use of electricaltransport and placement of component devices from a source to targetlocations, and to affix and, if required by the nature of the device, toactivate the device through cooperation with the target device ormotherboard.

In yet another aspect, these inventions seek to employ electricalforces, such as electrostatic, electrophoretic and electroosmoticforces, to transport, position and orient components upon a designedsubstrate.

In yet another aspect of this invention, the methods and apparatus aredesigned to optimally provide parallel actions, such as through theparallel transport of various component devices to multiple targetlocations.

It is an object of this invention to enable nanotechnology andself-assembly technology by the development of programmableself-assembling molecular construction units.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show DNA structure and its related physical dimensions.

FIG. 2 is a flow diagram of the overall process at one level ofgenerality.

FIG. 3 is a flow diagram of self-assembly processes.

FIG. 4A is a perspective drawing of the apparatus and method forredistribution of photonic devices fabricated as dense arrays onto thehost substrate without mother substrate layout constraints.

FIG. 4B is a perspective view of a clustering of nanospheres by DNAassisted self-assembly to form synthetic photonic crystals.

FIG. 5 is a plan view of the contact and lead portions of the targetsubstrate or motherboard.

FIG. 6 is a cross-sectional view of a light emitting diode (LED) adaptedto be transported through a fluidic medium to the target shown in FIG.5.

FIG. 7 is a plan view of a LED positioned adjacent locating electrodes.

FIGS. 8A, 8B and 8C show a motherboard and associated device forplacement and attachment, including fluidic flow paths, FIGS. 8A and 8Bshowing flow paths from a drive electrode and FIG. 8C showing the flowpath for the center electrode.

FIG. 9 is a perspective view of a flip-chip bonding arrangement whichconserves the geometrical dimensions leading to the coupling of smalldense arrays of specialty devices onto local regions of mother boards.

FIG. 10 shows a perspective view of global distribution of small densestructures from small dense chips on to less dense mother boards.

FIG. 11 shows a cross-sectional view of a structure for theself-assembly of micro or nanostructures utilizing a selective glue inwhich specialty devices of the given type are provided with a specificDNA polymer glue, the areas where these devices must attach beingcovered with the complimentary DNA glue.

FIG. 12 shows a cross-sectional view of selective electric fielddeposition of DNA onto the specially derivitized microelectrodesurfaces.

FIG. 13 shows a cross-sectional view of a micro or nanoscale structurecoupled to its host mother board substrate by selective DNAhybridization between complimentary DNA strands.

FIG. 14 shows a cross-sectional view of nanostructures held in place viaa DNA bond (left-hand side) and nanostructure held by a metallurgicalcontact after a high temperature cycle (right-hand side).

FIG. 15 shows a cross-sectional view of an apparatus for the orientationof specialty devices prior to hybridization by physical masking andcharge guiding.

FIG. 16 shows an apparatus for attachment and orientation of largersized devices onto a substrate or motherboard.

FIG. 17 shows an apparatus for fabrication of nanostructures.

IMPORTANT ASPECTS OF DNA STRUCTURE, PROPERTIES, AND SYNTHESIS

Synthetic DNA possesses a number of important properties which make it auseful material for the applications of these inventions. The mostimportant are the molecular recognition (via base pairing) andself-assembly (via hybridization) properties which are inherent in allDNA molecules. Other important advantages include the ability to easilysynthesize DNA, and to readily modify its structure with a variety offunctional groups. We have extensively investigated the photonic andelectronic energy transfer mechanisms in self-assembled arrangements ofsynthetic DNA functionalized with a wide variety of donor and acceptorchromophore groups. We have paid particular attention to the basicproblems involved in communicating or getting information in and out ofthese molecular structures. This basic work is now being applied topotential applications for high density optical storage materials, whichhave been designed to absorb light energy at a single wavelength andre-emit at predetermined multiple wavelengths. We are also now using DNApolymers for the two and three dimensional organization of micron andsubmicron sized structures on silicon surfaces. This work is beingdirected at the development of novel optoelectronic devices.

The DNA molecule is considered important to certain aspects of thisinvention and the proposed applications because it is inherentlyprogrammable and can self-assemble. Designing, synthesizing, andorganizing these systems requires nanometer range control which fewother synthetic polymer systems can match. Additionally, DNA moleculesare relatively stable and have a number of other attributes which makethem a preferred material for nanofabrication.

The underlying technology for DNA and other nucleic acid type polymerscomes from the enormous effort that has been invested over the pastfifteen years in synthetic nucleic acid chemistry. Molecular biologistshave refined techniques and DNA materials in their pursuit ofdiagnostics, genetic sequencing, and drug discovery. The basic chemistryfor the efficient synthesis of DNA, its modification, its labeling withligands and chromophores, and its covalent linkage to solid supports arenow well developed technologies. Synthetic DNA represents the preferredmaterial into which so many important structural, functional, andmechanistic properties can be combined.

DNA polymers have three important advantages over any of the presentpolymeric materials used for electronic and photonic applications.First, DNA polymers provide a way to encode highly specific binding-siteidentities or semiconductor or photonic surfaces. These sites, producedat defined locations, could be of microscopic (micron), sub-micron, oreven molecular (nanometer) dimension. Second, DNA polymers provide a wayto specifically connect any of these locations. The pre-programmed DNApolymers self-organize automatically. Finally, DNA polymers provide thebuilding blocks for nanotechnology; they are self-organizing materialsfor creating true molecular-level electronic and photonic devices.

The specificity of DNA is inherent in the hydrogen bonding properties ofthe base components (Adenine bonds only with Thymine, and Guanine bondsonly with Cytosine). These specific base pairing properties of DNA allowcomplementary sequences of DNA to “hybridize” together to form thedouble-stranded structure. It is this inherent property which allows DNApolymers to be used to form programmable self-assembling structures.Thus, when a photonic device has one specific DNA polymer sequenceattached to it, it will only bind (hybridize) to a device or surfacecoated with the complementary DNA polymer sequence. Since a largevariety of DNA sequences can be used, multiple devices, each attached toa different DNA sequence can in principle be self-assembledsimultaneously. The following lists the important advantages of usingDNA polymers for self-assembling nanofabrication applications:

1. DNA polymers can by synthesized both rapidly and efficiently withautomated instruments. Conventional polymer chemistries can besignificantly more complex and costly to develop.

2. DNA polymers can be synthesized in lengths from 2 to 150 nucleotides,which is the appropriate size range (1 nm to 60 nm) for self-assemblingunit cells.

3. DNA polymers can be synthesized with any desired base sequence,therein providing programmable recognition for an almost unlimitednumber of specific connections.

4. DNA polymers with unique sequences of as few as ten nucleotides arehighly specific and will bind only to their complementary sequence.Thus, the material allows specific connections as small as 3.4 nm to bemade between molecular units.

5. DNA polymers can be covalently labeled with fluorophores,chromophores, affinity labels, metal chelates, chemically reactivefunctional groups and enzymes. This allows important photonic andelectronic properties to be directly incorporated into the DNA polymers.

6. DNA polymers can be modified at any position in their sequence, andat several places within the individual nucleotide unit. This provides ameans to position functional groups for maximum performance.

7. DNA polymers can be both covalently and non-covalently linked tosolid surfaces: glass, metals, silicon, organic polymers, andbio-polymers. These attachment chemistries are both existing and easilydeveloped.

8. The backbone structure of the DNA molecule itself can be highlymodified to produce different properties. Thus, there is compatibilitywith existing semiconductor and photonic substrate materials.

9. Modified DNA polymers can be used to form three-dimensionalstructures, thus leading to ultra high density secondary storageschemes.

10. DNA polymers can be reversibly assembled and disassembled by coolingand heating, or modified to remain in the assembled state. This is acritical property for self-organizing materials as it allows for moreoptions in the manufacture of resulting systems.

11. The structural and organizational properties of DNA polymers(nucleic acids in general) are well understood and can be easily modeledby simple computer programs. Thus, more complex molecular photonic andelectronic devices can be designed.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a flow chart showing major components typically included inimplementation of these inventions. At one level of generality, theinventions utilize the combination of fluidics and electronics for thetransport and placement of a component device on a target device(sometimes referred to as a motherboard). Various modes of transportutilizing electronics, typically in a medium, most typically a fluidmedium, include electrophoretic transport, electroosmotic transport, anddielectrophoretic action, including orientation and transport.Electrostatic potentials may be utilized with or without the presence offluid. Electroosmotic transport is typically considered to be surfacephenomenon, and accordingly, such transport is typically found close tothe surface, most typically a charged surface, which results in a netfluid flow.

FIG. 2 identifies two primary components, a chip or motherboard 20 and acomponent device 22. Typically, the chip or motherboard 20 will includecertain design aspects, described below, which aid in the achieving ofthe functions of placement, attachment and activation, if required, ofthe component device 22. Similarly, the component device 22 is designedand fabricated to achieve the requirements of placement, attachment andactivation, if required. Typically, the component device 22 is deliveredat step 24 to the vicinity of the chip or motherboard 20. The componentdevice 22 may be delivered at step 24 in numerous ways, described below,though in the preferred embodiment, at least a portion of the deliverypath includes a fluidic delivery portion. The placement step 26 servesto position the component device 22 in proper relationship to the chipor motherboard 20 to permit the effective attachment and activation, ifrequired, of the component device 22. Attachment step 28 may be achievedby any technique consistent with the other stated goals in functions ofthe invention, though in the preferred embodiment comprising a solderreflow technique. Namely, solder previously positioned on the chip ormotherboard 20, and/or the component device 22 may be made to form aelectrical and mechanical attachment of the component device 22 to thechip/motherboard 20. Additional mechanical attachment structures orforces may be utilized as necessary. If required by the nature of thedevice, activation step 30 serves to permit electronic interactionbetween the chip or motherboard 20 and component device 22.

FIG. 2 includes certain specifics regarding the placement, attachmentand activation of a light emitting diode (LED) as a component device 22.A chip or motherboard 20 may be designed and fabricated such that theLED component device 22 may be attached to it and made active throughthe operation of the chip or motherboard 20. In one embodiment, the LEDcomponent device 22 is of a size (approximately 20 microns in diameter)and weight such that effective electrophoretic placement would not befeasible. Such transport would not be feasible if the charge to massratio necessary to effect electrophoretic transport was so high as tocause damage to the component device 22, or could not be achievedthrough placement of charge on the component device 22. In such a case,electroosmotic flow may be utilized, either alone or in combination withother forces (fluidic, electrostatic, electrophoretic and/ordielectrophoretic) in order to move the component device 22 relative tothe chip or motherboard 20 to achieve the desired placement. One theplacement step 26 had been achieved for the LED component device 22relative to the chip 20, electrical attachment may be achieved, such asin the preferred embodiment by performing a solder reflow step 28. Inthe case of an LED component device 22, provision of power from the chipor motherboard 20 may result in LED activation.

In certain embodiments, these inventions relate to methodologies,techniques, and devices which utilize self-assembling DNA polymers,modified DNA polymers, DNA derivitized structures and other affinitybinding moieties for nanofabrication and microfabrication of electronicand photonic mechanisms, devices and systems. This invention alsorelates to processes which allow multiplex and multi-step fabrication,organization or assembly of modified DNA polymers, DNA derivitizedstructures, and other types of affinity or charged structures into morecomplex structures on or within silicon or other surfaces. For purposesof this invention “DNA polymers” is broadly defined as polymeric oroligomeric forms (linear or three-dimensional) of nucleic acidsincluding: deoxyribonucleic acid, ribonucleic acids (synthetic ornatural); peptide nucleic acids (PNA); methyphosphonates; and otherforms of DNA in which the backbone structure has been modified toproduce negative, positive or neutral species, or linkages other thanthe natural phosphate ester. Also included are forms of DNA in which thesugar or base moieties have been modified or substituted, and polymericforms of DNA in which nucleotide or polynucleotide units areinterspersed with other units including but not limited to phosphateester spacer moieties, amino acids, peptides, polysaccharides, syntheticorganic polymers, silicon or inorganic polymers, conductive polymers,chromophoric polymers and nanoparticles or nanostructures.

For purposes of this invention “electroosmotic” is broadly defined as anaspect of electrophoresis where the electric field causes the relativemotion of water molecules and other entities to occur at or near acharged surface.

For purposes of this invention “electrophoretic” is broadly defined as aprocess for transporting electrically charged entities in solution usingan electric field.

For purposes of this invention “dielectrophoretic” is broadly defined asa process involving high frequency AC electric fields which causes therelative movement of molecules or other entities in solution.

For purposes of this invention “electrostatic” is broadly defined as thenet electric charge (positive or negative) on a molecule or otherentity.

For purposes of this invention “Modified or Derivitized DNA polymers”are broadly defined as nucleic acids which have been functionalized withchemical or biological moieties (e.g., amines, thiols, aldehydes,carboxyl groups, active esters, biotin and haptens) which allow the DNAto be attached covalently or non-covalently to other molecules,structures, or materials. Also included are forms of DNA which have beenmodified or Derivitized with chromophores, fluorophores, chelates, metalions, amino acids, peptides, proteins, enzymes, antibodies, or aliphaticor aromatic moieties which change solubility, and moieties which changethe net charge on the DNA molecule.

For purposes of this invention “DNA Derivitized structures” are broadlydefined as nanostructures (organic, inorganic, biological);nanoparticles (gold, silica, and other inorganic materials); organic orpolymeric nanobeads; submicron devices, components, particles, (siliconbased devices produced by photolithography or E-beam lithography); andmicron scale devices or particles which have been functionalized with aspecific DNA sequence which allows the structure to be specificallyattached or interconnected to another structure, device, or to aspecific location on a surface.

While the terms “nanostructure” refers to sub-micron sized structures,terms such as “nano” or “micro” are not intended to be limited in thesense that a micron scale device can be functionalized with DNA polymerswhich technically have lengths of 10-180 nanometers.

The unique properties of DNA provides a programmable recognition code(via the DNA base sequence) which can be used for specific placement andalignment of sub-micron and nanoscale structures. The basic chemistryand technology required to attach specific DNA sequences to organic,semiconductor, and metallic compounds is known to the art and specificchemistries are described for carrying out such applications.

This fabrication technique has major applications in the field ofoptoelectronics and in the manufacturing of various hybrid-integratedcomponents including flat panel displays, medical diagnostic equipmentand data storage systems. Novel devices with very small physicaldimensions take advantage of various quantum confinement techniques. Inmost cases, these devices are preferably distributed over large areas(e.g. smart pixels and displays). Other devices may be brought togetherin dense regular crystal lattices (e.g. photonic bandgap crystals). Inboth cases, the physics of the devices are now understood, and viablefabrication techniques of these inventions are required. With regard tonew processing techniques, DNA self-assembly technology allows thesedevices to be constructed.

Integrated photonic and electronic systems utilize the inventivefabrication technologies including nanostructure fabrication,integration, interconnection and self-assembly techniques. For suchapplications, DNA self-assembly fabrication technology involves thefollowing steps. Synthetic DNA polymers are designed with highlyspecific binding affinities. When covalently attached to nanoscaleorganic, metallic or semiconductor component devices, DNA polymersprovide a self-assembly fabrication mechanism. This mechanism can beused for both the selective grafting of devices to specificpre-programmed locations on a desired surface, and for the clustering ofdevices into pre-programmed 2 and 3 dimensional lattices.

For grafting an array of photonic component devices onto a hostsubstrates, DNA polymers with complementary sequences are firstsynthesized as shown in FIG. 2. The photonic component devices anddesired areas of the host substrate (receptor areas) are coated with thecomplementary DNA sequences. The host substrate is then introduced intoa hybridization solution. The devices coated with the specific DNApolymers are also released from their mother substrate into thesolution. The released devices can be actively transported to theirreceptor areas under the influence of electrically or optically inducedlocal fields (electrophoresis). Hybridization is carried out bycarefully controlling the solution temperature, ionic strength, or theelectric field strength. Once the devices are grafted via hybridizationto their specific receptor areas, the solution is removed and thesubstrate is dried. Metallurgical (or eutectic) bonding can now becarried out at a higher temperature to fully bond the devices to thehost substrate material. The clustering of sub-micron and nanoscaleelements into 2-D or 3-D structures (e.g., photonic band-gap crystals),can be carried out in a similar fashion. In this case, the hostsubstrate is replaced by other nanoscale elements. A major differencehowever, is the attachment technique used to position different DNAstrands on the nanoscale elements.

The self-assembly fabrication technique based on DNA polymers offers twounique features. First, by removing the requirement for conservation ofrelative device spacing (as defined by the mother substrate) during thedevice grafting (hybridization) process, the technique enables themicron, sub-micron or nanoscale devices to be fabricated densely ontheir mother substrates and then be redistributed in a preprogrammedfashion onto the host substrate (FIG. 4A).

This feature has a profound impact on the viability of intra-chipoptical interconnects within large chips. It lowers the cost of siliconbased smart pixels where photonic devices must be fabricated on moreexpensive smaller substrates. The second feature is the ability tomanipulate and orient with respect to each other a large number ofnanoscale devices (e.g. organic or metallic nanospheres). This featureallows the “growth” of synthetic photonic crystals with large latticeconstants possessing desired orientation symmetries for exhibitingphotonic bandgap properties (FIG. 4B).

Thus, the highly specific binding affinities and self-assembly of DNApolymers can lead to:

-   -   (1) Low cost smart pixels and display devices by enabling        photonic or electronic micron or nanoscale devices to be        self-assembled and integrated over very large areas of silicon        or other substrates, i.e. the self-assembly of an arrays of        light emitters on a silicon substrate,    -   (2) Highly selective wavelength and tunable devices by enabling        dielectric nanostructures to be self-assembled to form photonic        bandgap crystals, i.e. the encapsulation of emitter devices        within a photonic bandgap crystal layer created by the        self-assembly of DNA nanospheres,    -   (3) Ultra high density optical storage media by enabling        chromophore molecules and nanostructure units to be selectively        self-positioned, and    -   (4) The selective positioning of bonding structures, such as        gold, tin or solder structures as bonding pads, e.g., to achieve        low cost or unassisted die-to-die processing, e.g., for        flip-chip applications.

In the preferred embodiment, these applications require four steps inthe process. The first involves the design and synthesis of the DNApolymer sequences and their selective attachment to the sub-micron andnanoscale devices of interest. Second, attachment of specificcomplementary DNA polymers to pre-selected receptor locations on a hostsubstrate surface. Third, the self-assembly of the devices by the DNAhybridization process. The fourth process involves establishing theelectrical contacts.

This invention brings together molecular biological (DNA structure andfunction) and photonic and electronic device principles in a synergisticmanner. On the photonic device side, novel devices with very smallphysical dimensions take advantage of various quantum confinementtechniques. In most cases, these devices must be distributed over largeareas (e.g. smart pixels and displays). In other cases, these devicesmust be brought together densely to form regular crystal lattices (e.g.photonic bandgap crystals). With regard to processing techniques,self-assembly DNA techniques with its well developed base of DNAsynthesis, modification, and hybridization is an enabling technology forthese applications. DNA linkage to solid supports and various othermaterials is possible via a variety of processes for attaching DNAselectively to silicon, gold, aluminum and other inorganic and organicmaterials. A number of thin film processing techniques are highlycomplementary with these DNA processes. For example, as will bedescribed later, the lift-off process can be easily adapted to producemicron, and sub-micron devices with attached DNA sequences.

Experimental-Transport of LED as Component Device to a Motherboard

A light emitting diode (LED) has been transported and placed principallythrough electroosmotic force onto a target portion of a chip ormotherboard, electrically connected and mechanically attached thereto,and activated. FIG. 5 is a plan view of the contacts and structures onthe chip or motherboard. FIG. 6 is a cross-sectional drawing of acomponent device LED adapted to be placed, attached, and activatedthrough the contact structure of FIG. 5.

FIG. 5 shows a generally planar structure having a first electrode 52,second electrode 54 and lead 56 disposed on the surface or substrate 50of the chip or motherboard. The first electrode 52 is shown having ahorseshoe shape, being an annularly shaped electrode being substantiallycontinuous throughout the electrode region, and having two terminalends. The second electrode 54 may also be termed a center electrode orcontact or anode contact. As shown, the center contact 54 is directlyand electrically connected to lead 56. Lead 56 is disposed between, butspaced apart from, the terminal ends of the first electrode 52.

FIG. 6 shows one implementation of a light emitting diode/componentstructure 60. A substrate 62 includes a first layer 64 disposed thereon,and a second layer 66 in contact with the first layer 64. The interfacebetween the first layer 64 and second layer 66 serve to generate lightfrom the LED 60. The light is generally emitted from the LED 60 in adownward direction as shown in FIG. 6 through the substrate 62. A firstelectrode 68 is disposed on the device 60 so as to contact the secondlayer 66 and first layer 64. The first electrode 68 is generally annularin shape and forms a continuous ring or band around the device 60. Thesecond electrode 70 is disposed on the outward facing portion of thesecond layer 66. Generally, the second electrode 70 is of a circulardisk-like shape. The second electrode 70 comprises the anode contact forthe P-region which constitutes the second layer 66. The first electrode68 serves as the electrical contact for the first layer 64 whichconstitutes the end-region.

When placed in an assembled condition, the LED of FIG. 6 is positionedsuch that the first electrode 68 in its annular portion disposed on theoutward facing surface of the second layer 66 is in contact with thefirst electrode 52 of FIG. 5. The second electrode 70 contacts thecenter contact 54 on the substrate 50.

FIG. 7 shows a microphotograph in plan view of a target site and LED.The LED 72 is disposed above, and obscures, a center contact 54 andhorseshoe shaped cathode 52 (previously described in connection withFIG. 5). Lead 74 connects directly to the center contact 54 and lead 76electrically contacts the center contact 54 and lead 76 electricallycontacts the center contact. A first drive electrode 80 is disposedproximal to the target location for the LED 72. A second drive electrode84 is disposed in a mirror image relative to the transported device,that is, the LED 72. The drive electrodes 80, 84 are contacted with afirst drive electrode lead 82 and a second drive electrode lead 86,respectively. The leads 82, 86 serve to provide electrical contact tothe drive electrodes 80, 84 from a power supply and control system. Asshown in FIG. 7, each of the drive electrodes 80, 84 is quasi-kidneyshaped. Alternate shapes consistent with the functionality of transport,placement and/or attachment may be utilized. For example, sections of anannular ring may be utilized.

FIG. 8 is a cross-sectional, diagrammatic view of an advantageoustechnique for the placement or positioning of a movable component device90. A host device or motherboard 92 includes a surface 94. In operation,the surface 94 is generally disposed in an upward orientedconfiguration, and is adapted to receive the movable component device90. Ordinarily, the surface 94 is horizontally disposed, such that themovable component device 90 is subject to no or minimal lateralgravitational forces. In that way, the controllable electrical forces,e.g., electroosmotic force, serves to place the movable component device90 in the desired location. The surface 94 receives the solution,typically a buffer solution, in which the movable component device 90 isplaced.

FIG. 8 shows one advantageous mode of operation of a motherboard inorder to place a movable component device 90 at a desired electrodelocation 96. FIG. 8A shows the movable component device 90 disposedabove the surface 94 of the substrate 92. The electroosmotic flowcurrent 100 is shown moving in a generally rightward direction on thesurface 94 of the substrate 92. A drive electrode 98 is the activeelectrode for the creation of the electroosmotic current and flow 100.The movable component device 90 is subject to a lateral force in arightward direction, causing its motion toward the target location,namely, the electrode location 96. The electroosmotic flow 100 as itreaches the drive electrode 98 is in a generally upward direction. Asshown in FIG. 8B, the movable component device 90 has been moved intolocation above the electrode 96. The electroosmotic flow 100 path maythen be altered slightly based upon the physical presence of the movablecomponent device 90. The movable component device 90 may beapproximately positioned above the electrode 96 via the drive electrode98. FIG. 8C shows an advantageous technique for the placement of themovable component device 90 more precisely on the electrode location 96.By deactivating the drive electrode 98, and activating the electrodelocation 96 so as to cause electroosmotic flow in the general flowcurrent 102, the movable component device can be caused to beaffirmatively pressed to the electrode 96 through the action of theelectroosmotic flow and pressure generated therefrom. In this manner,the gross or rough positioning or placement of the movable componentdevice 90 through action of the drive electrode 98 may be achieved,followed by the precise positioning of the movable component device 90achieved through action of the electrode location 96.

Detailed Procedures For LED Placement and Attachment

Pretreatment

The electrode array chips undergo a O₂ plasma cleaning followed by a Arplasma cleaning step (10 min each). The chips are then placed in amedium sized plastic petri dish containing two droplets of water andabout 100 μl of(Heptadecafluoro-1,1,2,2-tetrahydrodecyl)dimethylchlorosilane (Gelest).The petri dish is partially covered and evacuated (house vacuum) forabout 15 min. The chips are placed in a clean glass petri dish and curedat 90 C for 15-30 min.

Plating

The active electrode area is determined for each chip by running acyclic voltamogramm (CV) in an aqueous solution of 0.1 M. K₂K₃Fe(CN)₆and 0.5 M KCl and comparing with the CV obtained from a 80 μm circularelectrode. The determined area is then used to calculate the necessarycurrent corresponding to 3.75 μA on a 80 μm circular electrode. The chipsurface is thoroughly rinsed with water and then covered with tin-lead(40:60) electroplating solution (Techni Solder Matte NF 820 HS, TechnicInc.) A constant current is applied for several seconds to produce thedesired plating height. The plating solution is immediately removed andreplaced by a 0.1M pH 5.2 sodium acetate buffer solution. Vigorousstirring is necessary to dissolve any precipitates. The chips isthoroughly rinsed with water and air dried.

LED Lift-Off

Standard Procedure

The GaAs substrate is removed from the attached Si wafer by heatingabove 100 C to melt the wax that is used for attachment. The freed GaAswafer is then soaked in dichloromethane for 15-45 min (to remove thewax), followed by a rinse with isopropanol and water. After drying thewafer is immersed in buffered HF (6:1) for 150 sec and then soaked inwater. After drying the wafer is immersed in conc. HCl for 60 sec andthen soaked in water. At this point usually a majority of the LEDs canbe removed from their sockets with a micromanipulator tip.

Modified Procedure

A short exposure (20 sec) to conc. HF/Ethanol 1:3 accomplishes lift-offeasily (many LEDs get removed from their sockets) without affecting theLEDs' performance.

Aging

LEDs once lift-off tend to re-adhere strongly to the substrate overtime. They can be re-released by short exposure (30 sec) to conc. HCl.

Plasma Cleaning

Plasma cleaning (Ar or O₂) has no effect on the lift-off of LEDs.However, it has an impact on the behavior of LEDs in solution. Ar plasmacleaned LEDs adhere strongly to the SiO₂ chip surface and can hardly beflipped gold side down. Once flipped they tend to flip back very easily.

LED Derivatization

Thiolacetic Acid/Thiolethylamine

New LEDs are first soaked in acetone followed by isopropanol and waterand then air dried. Used LEDs are O₂/Ar plasma cleaned (10+10 min). Thecleaned LEDs (on their substrate) are immersed in 1-10% solutions of therespective thiol in 1:1 isopropanol/water for 60-120 min and then soakedin 1:1 isopropanol/water followed by water.

Silanes

Prior to deposition the LEDs are O₂ plasma cleaned (10 min). Volatilesilanes are deposited as vapors at ambient or reduced pressure for 15min. Curing is performed at 90 C for 15-30 min.

Non-volatile silanes are deposited from 2% solutions in 200 proofethanol (10 min). After deposition the samples are rinsed with ethanoland cured at 90 C for 15-30 min.

LED Transfer

Standard Procedure

A water soluble glue is prepared by mixing 5-6 g of Ficol 400 into 2.5ml glycol and 0.5 ml water. This mixture is very hygroscopic andrelatively quickly changes its consistency. Ideally, the glue shouldstay at the tip of a fine micro-manipulator tip without wicking back bycapillary force. LEDs are removed from their sockets with a clean probetip. The very tip of the probe is brought in contact with the glue. Aminimal amount of glue is used to pick-up and transfer the LED. Theprobe tip with the LED is moved to the surface of a dry chip. Water isadded to the chip and the LED is released from the probe tip due todissolution of the glue. The probe tip is removed and cleaned. The chipis rinsed 2× with water, soaked for 1 min and then rinsed once more(Eppendorf pipette). After removal of the water, 10 mM aminocaproic acidsolution is added to the chip. If the LED is oriented the wrong way, itcan be flipped either by introducing turbulence with a probe tip or bymoving the LED close to an electrode followed by application of a shortpulse of current (100-200 nA).

LED Movement and Alignment

LEDs that are oriented with their gold contacts facing upwards tend tostick to the surface and do not move. If the gold contacts are facingtowards the substrate surface the LEDs tend to hover and can be easilymoved (electronically, by probe tip movement or by convection).

In 10 mM ε-aminocaproic acid currents of about 100-300 nA are sufficientto move an LED across several hundred microns.

Standard Procedure:

A cathodic current (100-300 nA) is applied to one of the two driveelectrodes (the one that is more distant from the LED) using the ringelectrodes as counter electrodes. As soon as the LED starts acceleratingtowards the electrodes, the current is continuously adjusted to maintaina steady movement. (If the movement is too slow the LEDs can get stuckto the surface. If the movement is too fast the LEDs can get flipped invicinity of the electrodes.) Once the LED is close to the space betweenthe two drive electrodes, the second drive electrode is activatedwithout increasing the current. At this point current levels of about10-30 nA should be sufficient to keep the LED close to the contactelectrodes. By varying the current at low levels (5-15 nA) the LED iscentered above the contact electrodes. Once the LED is centered, theouter contact electrode is activated as counter electrode while the ringelectrodes are disconnected. The current (2-15 nA) now flowing betweenthe drive electrodes and the outer contact electrode forces the LED downonto the surface. If the LED is not sufficiently centered the previousstep is reverted and then repeated. Immediately after this step theliquid is removed and the electrodes disconnected (over time largercurrents are needed to keep the LED positioned).

Contact Formation

Standard Procedure

The LED/substrate assembly is air dried and then exposed to an Ar plasma(ca. 250 W at 250 mTorr) for 10 min. This process physically attachesthe LED to the contact electrodes. A few microliters of flux(Alphametals 2491-121) are applied to the surface. The sample isenclosed in a reflow chamber that is purged with a gentle flow offorming gas (95% N₂, 5% H₂). The flux solvent is dried off at 60 C untilthe solid flux components precipitate. The sample is then heated at arate of about 90 C/min to a final temperature of 250 C. The heater isturned off and the forming gas flow is increased to let the sample cooldown.

Electric Field Assisted Assembly Under Low Gravity Conditions

One aspect of this invention concerns the potential to improve theperformance of electric field assisted pick and place processes forheterogeneous integration under low gravity conditions. Low gravityconditions would allow the pick the electric field assisted processes tobe carried out under overall lower field conditions than under normalgravity. Thus, larger and heavier micron-scale objects could now betransported, orientated, and positioned much more effectively then undernormal gravity conditions. Thus, the electric field assisted processesmay prove more useful and viable when carried out in space platforms(space stations) were low gravity conditions exist. In another aspect ofthis invention electric field assisted assembly under low gravityconditions may be carried out without the need for a fluidicenvironment, by using controlled electric fields to transport andmanipulate objects which have an electrostatic charge.

Key Processes for DNA Based Component Device Self-Assembly

Four techniques are important for the DNA based component deviceself-assembly process. These are the DNA polymer synthesis, DNAattachment chemistry, DNA selective hybridization and epitaxial lift-offof semiconductor thin films and devices. In the following sections weprovide brief summaries of these techniques.

DNA Synthesis and Derivatization

The synthesis of the DNA polymer or oligomer sequences, theirpurification, and their derivatization with the appropriate attachmentand chromophore groups can be carried out in the following preferredmanner: DNA sequences are synthesized using automated DNA synthesizerand phosphoramidite chemistry procedures and reagents, using well knownprocedures. DNA polymers (polynucleotide, oligonucleotides, oligomers)can have primary amine groups incorporated at chemical bonding sites forsubsequent attachment or functionalization reactions. These primaryamine groups can be incorporated at precise locations on the DNAstructure, according to the need for that particular sequence.Attachment sequences can also contain a terminal ribonucleotide groupfor subsequent surface coupling reactions. Sequences, including theamino modified oligomers, can be purified by preparative gelelectrophoresis (PAGE) or high pressure liquid chromatography (HPLC).Attachment sequences with terminal amino groups can be designed forcovalent bonding to gold, silver, or aluminum metalized features or tosmall areas where silicon dioxide is present. These sequences can befurther Derivitized with a thiolation reagent called succinimidyl3-(2-pyridyldithio)propionate (SPDP). This particular reagent produces asequence with a terminal sulfhydryl group which can be used forsubsequent attachment to metal surfaces. Other attachment sequencescontaining a terminal ribonucleotide group can be converted to adialdehyde derivative via Schiffs base reaction. These attachmentsequences can then be coupled to aminopropylated silicon dioxidesurfaces. Specific sequences designed for electronic or photonictransfer responses can be functionalized with their appropriatechromophore, fluorophore, or charge transfer groups. Many of thesegroups are available off-the-shelf as activated reagents that readilycouple with the chemical bonding sites described above to form stablederivatives.

DNA Attachment to Solid Supports and Preparation of the Host SubstrateMaterials

This step involves the covalent coupling of the attachment sequences tosolid support materials. In the general area of DNA attachment to solidmaterials, sequences have been covalently attached to a number ofmaterials which include: (i) Glass (SiO₂), (ii) Silicon (Si), (iii)Metals (Gold, Silver, Aluminum), and (iv) Langmuir-Blodgett (LB) films.Glass, silicon, and aluminum structures have been prepared in thefollowing manner. Glass and silicon (SiO₂) are first treated with dilutesodium hydroxide solution and aluminum with dilute hydrogen fluoridesolution. The materials are then Derivitized for covalent coupling withthe attachment sequences by treatment with 3-aminopropyltriethoxysilane(APS). This is carried out by refluxing the materials for 2-5 minutes ina 10% APS/toluene solution. After treatment with APS, the materials arewashed once with toluene, then methanol, and finally dried for 1 hour at100° C. Attachment to the APS Derivitized materials is carried out byreaction with the specific dialdehyde Derivitized attachment oligomers(see FIG. 4) for 1-2 hours in 0.1 M sodium phosphate buffer (pH 7.5). Inaddition, attachment to metal (gold, silver, aluminum) and organicfeatures can be carried out.

To delineate the areas where the grafting of the specialty devices willtake place, a selective attachment procedure for the complementary DNApolymer may be carried out. The selective attachment can be realized byusing the inherent selectivity of DNA sequences, selective attachmentchemistries, or by directed electrophoretic transport. Alternativelyafter attachment, the DNA strands in unwanted regions can be destroyedby UV radiation. This approach is useful only when one group of devicesneed to be self-assembled. This approach would in normal operationpreclude subsequent DNA attachment processes, and would not allow forthe self-assembly of several specialty device groups. Attachmentchemistry is strongly dependent upon the materials used to which the DNApolymers may be attached.

For example, to attach DNA to aluminum pads on a silicon chip coatedwith a protective glass layer, the aluminum regions are activated bydipping the sample for a short period of time into a dilute buffered HFsolution. The end result of this process is that only a few DNA strandsare attached to the protective glass layer while the exposed aluminumpads are highly reactive to DNA. This material selectivity is aconvenient and general way to attach DNA to the desired regions. Whenmaterial selectivity is combined with UV directed inactivation andelectrophoretic transport, this allows for repeatable attachmentprocesses to be carried out sequentially.

Consider the simultaneous self-assembly of several types of specialtydevices. The receptor pads need to be grouped according to the device towhich they are to be coupled. In this case, each pad group needs to becoated with a specific DNA sequence complementary to the DNA sequenceattached to the specialty device that it would be bonded to. In order to“pre-program” the receptor pads, each DNA sequence is attachedsequentially to the proper pads. This can be easily achieved by usingthe electrophoretic transport process and by applying a negativepotential to the pads where DNA attachment is not desired.Simultaneously, a positive voltage can be applied to enhance attachmentto the desired locations. Alternatively, an optically induced electricfield can be used to migrate the DNA strands to desired locations. For asecond set of DNA sequence attachment, the procedure is repeated. Itshould be pointed out that when only one type of device needs to beself-assembled on the host substrate, the use of the materialselectivity of the DNA attachment chemistry alone is sufficient. UVradiation of the regions where DNA hybridization is not desired, wouldbe carried out.

Component Device Preparation and Epitaxial Lift-Off

Another key step for the self-assembly process is the preparation of thesub-micron and micron-scale component devices for DNA attachment, theirhandling during the attachment process, and their final release intosolution prior to hybridization. The epitaxial lift-off (ELO) processcan substantially improve these aspects of this technique. Epitaxialfilms in the thickness range of 20 nm to 10 mm have been separated fromtheir growth substrates, handled and manipulated. For example, usingthis technique thin III-V semiconductor films have been direct-bonded toforeign substrates, such as processed silicon wafers. Prior to lift-off,various devices can be fabricated on the films while still on theirmother substrates. The first step in our self-assembly technique is thepreparation of the photonic devices that are to be grafted. FIG. 5describes a preferred process flow for this preparation step. Thephotonic devices are fabricated in a standard fashion on their mothersubstrates on a sacrificial layer as required by the ELO process. Asuitable coating layer is then deposited on these devices. Bycontrolling the characteristics of the deposited material with respectto device materials the behavior of the devices once released into thesaline solution can be controlled. For example, by controlling thecoating material properties the direction of the devices in the solutioncan be controlled. A thick polyamide film is spun to provide a physicalsupport to the devices after the ELO process. The ELO process is carriedout and the thin film devices are separated from their mothersubstrates. By using plasma etching, the polyamide holding membrane isrecessed in areas with no devices. If needed, a metal layer can bedeposited to assure good electrical contacts to the photonic devices.The DNA attachment process is then carried out and a specific DNAsequence is covalently attached on all metal surfaces. By irradiatingthe front surface with a UV light, the photonic devices are used as aself-aligned mask enabling exposure of polyamide areas coated with DNApolymer. In these areas, the DNA polymers react to a form that is notsuitable for further hybridization. By using a solvent, the polyamidemay then be removed and the devices released into the saline solutionused for the further hybridization processes.

Selective DNA Hybridization Techniques

Once the host substrate is pre-programmed and the component devices arereleased into the solution, the self-assembly process can take place.Two different approaches for hybridization are applicable: (1)Conventional hybridization and (2) Active hybridization using anelectric field.

For the conventional hybridization process, all devices may be releasedsimultaneously into the solution. By gently agitating the devices in thesolution at the proper hybridization stringency temperature and ionicstrength, hybridization of the complementary DNA strands takes place asthe proper device-receptor pairs come into contact. The probability ofhybridization taking place may be related directly to the probability ofthe proper device-host pad pairs coming into contact. Since theprobability distribution is most likely random, this process may takelonger to achieve reasonable hybridization yields on large area surfacesunless the solution is saturated with the devices. In order to improvethe selectivity and alignment accuracy several controlled heating andcooling cycles may be carried out during the hybridization process.During the heat cycle, weakly hybridized components are dissociated awayto increase the chances of forming stronger bonds.

For active or electronic hybridization, the motherboard itself oranother electrode array manufacturing device are used to producelocalized electric fields which attract and concentrate selectedcomponent devices at selected locations. For this process themotherboard or manufacturing device has sites which can be used as anelectrodes. A potential is applied across the solution between selectedreceptor sites and auxiliary electrodes. Receptor sites biased opposite(+) to the net charge (−) on selected devices, now affect theelectrophoretic transport and concentration of these devices therebyincreasing the rate of hybridization and binding. These sites can beselectively switched on or off using electronic or photonic addressing.A pulsing DC or biased AC electric field can be applied at a suitablefrequency to eliminate the screening effect of the unwanted devicetypes.

The electric field effect can also be used in a protective manner. Inthis case, the receptor pads are now biased the same (−) as the netcharge (−) on the devices. The devices are then repelled from theseregions and interact or bind only to those locations which have theopposite charge (+) or are neutral. Active electric field transport canbe used to carry out multiplex and multi-step addressing of componentdevices and structures to any location on the motherboard array.

Another important consideration during hybridization is the alignmentaccuracy of the photonic devices on the motherboard or host substrate.It is assumed cylindrical photonic devices that rotation is invariant.In this case, if the device and host pad diameter is d, an alignmentaccuracy of d/2 may be first achieved with the natural hybridizationprocess prior to the drying process. Devices that are mis-aligned withmore than d/2 misalignment will not form a strong bond during thehybridization process and will not be held in place during the heatingand cooling cycles of the hybridization process. Better alignmentaccuracy and orientation are possible when active electric fieldhybridization is used. Once the substrates are removed from thesolution, increased surface tension during the drying process couldfurther improve the alignment accuracy.

Metallurgical Bonding

After the hybridization process the specialty devices are held in theirproper places through the formation of the double-stranded DNA structurewhich has a very high bonding strength. The entire assembly is thencleaned by rinsing and then dried. The DNA bond strength remains in thesolid state and serves to keep the devices in place. At this point ofthe process, there is however, no electrical contact between the hostsubstrate and the photonic devices. One method to achieve ametallurgical bond exhibiting an ohmic contact between the hostsubstrate and the photonic devices is to use conductive materials on thepads and devices that can be bonded together eutectically at lowtemperatures. A second method is to use metals with low meltingtemperatures like solder or indium under a metal layer that is activefor DNA attachment. While the photonic devices are held in place by theDNA bonds, the application of heat will result in the formation of ametallurgical bond. The DNA polymer will disintegrate within the bondbut may only contribute to an increased contact resistance depending onthe initial DNA loading factor used.

Development of Self-Assembled Emitter Arrays

As one example of the utility of these inventions, emitter arrays can beadvantageously formed. Specific DNA polymer sequences may be covalentlyattached to semiconductor light emitting diodes (LED) and thecomplementary DNA sequences may be attached to receptor pads on the hostsilicon substrate. UV/DNA patterning techniques may be used forselective activation/inactivation of DNA on the coated surfaces. All DNADerivitized test structures and materials will then be tested forselective hybridizability using complementary fluorescent DNA probes.LED test devices Derivitized with specific DNA sequences may behybridized to test substrates Derivitized with complementary DNAsequences.

Development of Self-Assembled Photonic Band-Gap Structures

Photonic or crystals may be formed using the DNA self-assemblytechnique. Photonic Bandgap Structures are artificial periodic latticestructures in two- or three-dimensional arrangements and composed ofelements of proper dimensions, density and separations. Such structuresresult in the modification of photonic density of states and a gap inthe electromagnetic wave dispersion. Indeed, photonic bandgap structuresoperating at specific optical wavelengths have been demonstrated.Potential applications of photonic bandgap materials include tailoringof the spontaneous emission of a laser to achieve ultra-low thresholdlazing, improved wave guiding structures without radiation loss, noveloptical modulators, etc.

The various DNA polymer (oligonucleotide) sequences described above, inthe 20-mer to 50-mer size range, may be synthesized on automated DNAsynthesizers using phosphoramidite chemistry. Longer DNA sequences aregenerally required to bind larger objects to surfaces because thebinding force must be sufficient to overcome forces (e.g., shearingforces) tending to remove the object. Longer DNA sequences (>50 mers)may be constructed using the polymerize chain reaction (PCR) technique.The DNA sequences may be further Derivitized with appropriate functionalgroups (amines, thiols, aldehydes, fluorophores, etc.). All sequencesmay be purified by either PAGE gel electrophoresis or HPLC. Afterpurification, all sequences may be checked on analytical PAGE gels forpurity, and then tested for specificity by hybridization analysis.

Several DNA sequences may be used to develop and test additionalchemistries for the covalently attachment to various, organic polymerbased nanospheres, semiconductor, and other material substrates (glass,gold, indium tin oxide, etc.). Additional attachment chemistries providemore options and flexibility for attachment selectivity to differentsemi-conductor materials.

Specific DNA polymer sequences may be covalently attached tosemi-conductor test structures and the complementary DNA sequences totest substrate (motherboard) materials. UV/DNA patterning techniques maybe used for selective activation/inactivation of DNA on the coatedsurfaces. All DNA Derivitized test structures and materials will then betested for selective hybridizability using complementary fluorescent DNAprobes.

Nanospheres, nanoparticles, and semi-conductor test structuresDerivitized with specific DNA sequences will now be hybridized usingboth conventional (temperature, salt, and chaotropic agents) andelectronic (electrophoretic) techniques to the test substrates(motherboards) Derivitized with complementary DNA sequences. Thehybridization techniques may be optimized for highest selectivity andleast amount of non-specific binding.

Fabrication of an LED Array

Specific DNA polymer sequences may be covalently attached tosemi-conductor light emitting diode (LED) component devices and thecomplementary DNA sequences to motherboard materials. UV/DNA patterningtechniques may be used for selective activation/inactivation of DNA onthe coated surfaces. LED component devices Derivitized with specific DNAsequences are then hybridized to test substrates (motherboards)Derivitized with complementary DNA sequences.

Self-Assembly Fabrication of a Photonic Crystal Structure

Multiple specific DNA polymer identities may be incorporated intonanoparticles or nanospheres for the self-assembly around emitter testdevices located on motherboard materials. UV/DNA patterning techniquesmay be used for selective activation/inactivation of DNA on the coatedsurfaces. Nanoparticles Derivitized with specific DNA sequences will nowhybridized to the emitter test devices located on the substrates(motherboards) Derivitized with complementary DNA polymers.

Further Aspects of Self-Assembly

This invention provides for assembling specialty devices in parallel andover larger areas (up to several meters on a side) using a“self-assembly” technique. In this approach, each device to be graftedsomehow “knows” where it is destined to be on the motherboard. Thisinvention relates to a new integration technique based on programmableself-assembly principles encountered in biological systems. This newtechnique removes the requirement of dimension conservation during thegrafting process. Our objective is to demonstrate the self-assembly ofmicro/nano structures on silicon using DNA (Deoxyribonucleic Acid)polymers as “selective glues”, thereby developing techniques forintegrating these structures sparsely onto large area motherboards. Thisbrings together with high precision, at low cost, devices made ofdifferent materials with different real densities as shown in FIG. 10.This approach relies on the principles of programmable self-assemblyfound in all biological systems, and uses existing well-understoodsynthetic DNA chemistry as the enabling process. These techniquesinclude: 1) remove the specialty devices from their mother substratesusing the epitaxial lift-off process, 2) attach selective DNA polymersequences onto the specialty devices using DNA attachment chemistryspecially developed in our company, 3) selectively attach complementaryDNA polymer sequences to proper locations on the motherboard substrate,and 4) carry out self-assembly by using hybridization of thecomplementary DNA strands. This uses DNA polymer sequences as a smartand very selective glue to attach micron/nanosize specialty devices todesignated areas on a motherboard (see FIG. 11).

Selective DNA Hybridization and Electric Field Transport Techniques

Techniques for the hybridization of DNA sequences to complementary DNAsequences attached to solid support materials are well known and used inmany biotechnologicai, molecular biology, and clinical diagnosticapplications. In general hybridization reaction are carried out inaqueous solutions which contain appropriate buffer electrolyte salts(e.g., sodium chloride, sodium phosphate). Temperature is an importantparameter for controlling the stringency (specificity) and the rate ofthe hybridization reactions. Techniques exist for hybridization of DNAsequences to semiconductor materials. The first is a UV lithographicmethod which allow imprinting or patterning of DNA hybridization ontosolid supports materials such as silicon dioxide and various metals. Thesecond is a method for electrophoretically transportingDNA-nanostructures (nanostructures to which specific DNA sequences areattached) to selected locations on substrate materials. The techniquefor UV lithography with DNA involves first coating a substrate materialwith a molecular layer of specific attachment DNA polymer sequences. Anappropriate mask can be used to imprint a pattern into the attachmentlayer of DNA by exposure to UV irradiation (300 nm) for several seconds.The DNA in the area on the substrate exposed to UV light becomesin-active to hybridization with its complementary DNA sequence i.e., itis not able to form the double-stranded structure. FIG. 7 showfluorescent DNA on a silicon structure was patterned with 10 micronlines using an electron microscope grid pattern. After UV patterning thematerial is hybridized with a complementary fluorescent labeled DNAprobe, and examined epifluorescent microscopy. The fluorescent imageanalysis shows where the complementary probe has hybridized(fluorescent), and where no hybridization has occurred (nofluorescence). In addition to DNA based UV photolithographic typeprocesses, other electric field based process allows derivitized DNA andcharged fluorescent nanospheres to be electrophoretically transportedand deposited onto selective microscopic locations on solid supports.The basic method and apparatus for this technology is shown in FIG. 12.Negatively charged DNA, sub-micron or micron-scale structures can besuspended in aqueous solutions and transported via an electric field(electrophoresis in solutions) to microscopic locations which are biasedpositive, relative to other locations which are biased negative. This isa particularly important technique in that it provides a mechanism todirect the transport of specifically labeled devices to specificlocations on a substrate material.

Micron/Nanoscale Structure Preparation

The first step in our self-assembly technique is the preparation of thespecialty devices to grafting. In this case, the specialty devices arefabricated in a standard fashion on their mother substrates on asacrificial layer as required by the ELO process. A suitable coatinglayer is then deposited on these devices to assure they have a Brownianlike motion in the saline solution. By controlling the characteristicsof the deposited material with respect to device materials the behaviorof the devices once released into the saline solution can be controlled.For example, by controlling the coating material properties we couldcontrol the direction of the devices in the solution. Once the devicesare coated, a thick polyamide film may be spun to provide a physicalsupport to the devices after the ELO process. The ELO process may becarried out and the thin film devices may be separated from their mothersubstrates. By using plasma etching the polyamide film may be recessedto provide sufficient steps to prevent the metal layer from beingcontinuous. The DNA attachment process is then carried out and aspecific DNA sequence may be covalently attach on all the metalsurfaces. By irritating with a UV light from the front surface of thedevices, the DNA areas that are exposed and not protected, may bedestroyed or put in a form that is not suitable for furtherhybridization. By using a proper solvent the polyamide will then beremoved and the devices may be released into the saline solution usedfor the further hybridization processes.

Preparation of the Motherboard Substrate

To delineate the areas where the grafting of the specialty devices willtake place, a selective attachment procedure for the complementary DNApolymer must be carried out. The selective attachment can be realized byusing the inherent selectivity of DNA sequences, selective attachmentchemistries, or by directed electrophoretic transport. Alternativelyafter attachment, the DNA strands in unwanted regions can be destroyedby UV radiation. This approach is useful only when one group of devicesneed to be self-assembled.

As described in earlier sections, DNA attachment chemistry is stronglydependent on the materials used to which the DNA polymers may beattached. For example, to attach DNA to aluminum pads on a silicon chipcoated with a protective glass layer, we first activate the aluminumregions by dipping the sample for a short period of time into a dilutebuffered HF solution. The end result of this process is that only a fewDNA strands are attached to the protective glass layer while the exposedaluminum pads are highly reactive to DNA. This material selectivity is aconvenient and general way to attach DNA to the desired regions. Whenmaterial selectivity is combined with UV directed inactivation andelectrophoretic transport process, this allows for repeatable attachmentprocesses to be carried out sequentially. Consider the simultaneousself-assembly of several types of specialty devices. The pads need thento be grouped according to the device to which they are to be coupled.In this case, each pad group needs to be coated with a specific DNAsequence complementary to the DNA sequence attached to the specialtydevice that it would be bonded to. In order to “pre-program” themotherboard pads, each DNA sequence can be attached sequentially to theproper pads. This can be easily achieved by using the electrophoresisprocess and by applying a negative potential to the pads where DNAattachment is not desired. Simultaneously, a positive voltage can beapplied to enhance attachment to the desired locations. For a second setof DNA sequence attachment, the procedure may be repeated with adifferent set of programming voltages. Thus, when the self-assembly ofmultiple device types need to be carried out simultaneously, themotherboard receiving pads may be programmed by applying a proper set ofpositive and negative potentials to the pads. When only one type ofdevice needs to be self-assembled on the motherboard, the use of thematerial selectivity of the DNA attachment chemistry alone issufficient.

Specific DNA Polymers: a Selective Glue

Once the motherboard is pre-programmed and the specialty devices arereleased and are freely moving in the saline solution bath, theself-assembly process can take place. At the proper (hybridization)stringency temperature, and by agitating gently the devices in thesolution, hybridization of complementary DNA strands may be allowed totake place as the proper device-pad pairs come into contact (see FIG.13). To achieve this process several different methods may beinvestigated.

Conventional and Electronic Hybridization

In this methods all devices may be released simultaneously into thesolution, and the probability of a hybridization process taking placemay be related directly to the probability of the proper device-padpairs to come into contact. Under very simplifying assumptions, theprobability of a hybridization P_(h) may be roughly related to the ratioof the total available pad area A_(p) to the mother board area A_(mb)P_(h) □NA_(p)/A_(mb)where N is the real density of one of the specialty device groups in thesolution. Since the probability distribution is expected to be random,this process may take very long times to achieve reasonablehybridization yields. Alternatively it may require the solution to besaturated with the specialty devices. This may increase the cost of theprocess and limit the number of types of specialty devices that can beself-assembled. In order to improve the selectivity and alignmentaccuracy several heating and cooling cycles will be carried out duringthe hybridization process. During the heat cycle, weakly hybridizedcomponents may be dissociated away to increase the chance of formingstronger bonds.

Epitaxial Lift-Off Process

A key part of the self-assembly process is the preparation of themicro/nano scale devices for DNA attachment, their handling during theattachment and finally their release into the saline solution prior tohybridization. The most popular ELO approach is to employ theselectivity of dilute HF acid on the Al GaAs series of alloys. TheAluminum rich alloys etch at a rate of approximately 1 mm/hr, while theetch rate of Gallium rich alloys is almost undetectable, less than 0.1nm/hr. An intermediate layer of AlAs dissolves, allowing upper epitaxiallayers to simply float away from the substrate. Other separation methodshave also been used, including mechanical cleavage (CLEFT), and totalsubstrate etching down to an etch stop layer. Epitaxial films in thethickness range between 20 nm and 10 mm have been separated from theirgrowth substrates, handled and manipulated.

For example, using this technique thin III-V semiconductor films havebeen direct-bonded to foreign substrates, such as processed siliconwafers. The mechanical flexibility of ELO films allows a perfectconformation of the films to the substrate topography, which creates astrong and complete bond. The ELO technique then, produces amonolithic-like epitaxial thin film on an engineered substrate. Prior tolift-off, various devices can be fabricated on the films while still ontheir mother substrates. The ELO technique stands somewhere intermediatebetween a hybrid approach, such as flip-chip solder bump mounting, and afully monolithic approach, such as direct hetero-epitaxy; it combines,however, the advantages of both. ELO is a true thin-film technology,allowing thin-film metal wiring which passes back and forth over theedge of a thin III-V film and onto a silicon micro-chip substrate. Atthe same time, the thin film is grown lattice-matched and essentiallyhomo-epitaxially. Material quality, of the utmost importance forminority carrier devices such as light emitters, is never compromised.Advantages of the ELO technology over hybrid flip-chip technologyinclude low packaging capacitance and high packing density. For highspeed micro-circuits, wiring capacitance must be very low. The penaltyis not merely the burden of added power dissipation. Since the seriesresistance of metal interconnects is not negligible, the RC timeconstant will ultimately act to limit the speed of opto-electronicmicro-circuits irrespective of power dissipation problems, severe asthey might be. The ultimate achievable packing density is somewhatscaled with respect to the working dimension of technologies. Therefore,the ELO may offer more in this aspect than the solder bump technique.

ELO films grafting on processed silicon micro-circuits requiresconsideration of the ultra-fine scale roughness of the deposited oxidesurfaces of the micro-chip. Surface roughness interferes with thequality of the Van der Waals or metallurgical bond.

Sequential Hybridization Under DC Electric Field

To increase the probability of hybridization, a second method is tointroduce each device group separately and to confine the specialtydevices within regions near the positively biased pads. This confinementcan be done under the influence of a DC electric field by applying asuitable positive voltage to the pads. The effect of the electric fieldcan then be viewed as increasing the ratio of the areas, or equivalentlyincreasing the device density, N, in the above equation. However, inthis case each device group must be introduced sequentially, so theunwanted device groups do not screen the right devices from reaching thepad.

Parallel Hybridization Under an AC Electric Field

The disadvantage of the sequential hybridization is that it increasesthe cost of manufacturing as the types of specialty devices isincreased. An alternative method is to introduce all device typesconcurrently into the solution, to apply an initial DC voltage to createa distribution of the devices around each pad, and then to apply an ACvoltage at a suitable frequency to eliminate the screening effect of theunwanted devices types. The effect of the AC field can be seen as astronger stirring mechanism.

Metallurgical Bonds

After the hybridization process the specialty devices are held in theirproper places through the formation of the double-stranded DNA structurewhich has very high bonding strength. The entire assembly is thencleaned by rinsing and then dried. At this point there is no electricalcontact between the motherboard and the specialty devices. The DNA bondstrength remains in the solid state and serves to keep the devices inplace. One method to achieve a metallurgical bond with ohmic contact isto use conductive materials on the pads and devices that can be bondedtogether eutectically at low temperatures. A second method is to usemetals with low melting temperatures like solder or indium under a metallayer that is active for DNA attachment. In this case the bumps must bemade in nanometer dimensions. While the device are held in place by theDNA bonds, in both cases the application of heat will result in theformation of a metallurgical bond and an ohmic contact. The DNA polymerwill remain within the bond but may only contribute to an increasedcontact resistance depending on the initial DNA loading factor used.FIG. 14 shows a the process described above.

Alignment and Orientation of the Specialty Devices

One of the critical issues that needs to be addressed in theself-assembly approach is the accuracy with which the specialty devicescan be aligned to the pads on the motherboard. We will first assume thatthe specialty devices have a circular base such that the process isrotation invariant. In this case, it is expected that if the paddiameter is d, an alignment accuracy of d/2 could be achieved with theDNA bonding process. Devices that are misaligned with more than d/2misalignment will not form a strong bond during the hybridizationprocess and would not be held in place during the heating and coolingcycles of the hybridization process. In addition, if the nano-bumptechnology outlined in the previous section is employed, after the hightemperature cycle for forming the metallurgical bonds, the devices maybe self-aligned to the pads in a similar fashion as with the C4technology used for flip-chip bonding.

A more difficult issue arises if the specialty device do not have acircular symmetric base and need to be placed with a certain orientationon the pads. Two different approaches for bonding with the properorientation may be used. As a first approach, properly patterned silicondioxide layers are used to physically mask out specialty devices withthe wrong orientations as shown in FIG. 15. The devices will fit ontothe pads only if they possess the right orientation. Another approach toorient the device is to use coulombic forces prior to the hybridizationof DNA. By ion implantation, or e-beam lithography exposure an oppositesign charge build-up can be realized in certain locations on the padsand on the devices. These charge patterns guide the devices to theirproper orientations. As can be seen in FIG. 15, both approaches can beused together to provide DNA bonding with proper orientation of thespecialty devices.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity andunderstanding, it may be readily apparent to those of ordinary skill inthe art in light of the teachings of this invention that certain changesand modifications may be made thereto without departing from the spiritor scope of the appended claims.

1. A method for the self-assembly of microscale and nanoscale devicescomprising the steps of: providing a host substrate, preparing the hostsubstrate for attachment of DNA polymers, patterning the host substrate,attaching DNA polymers to the patterned host substrate, fabricating acomponent device, placing the component device into a fluid mediumcontaining the host substrate, subjecting the component device to anepitaxial lift off process, attaching DNA polymers to the componentdevice, wherein at least a portion of the sequence of the DNA polymersare complementary to the DNA polymers attached to the patterned hostsubstrate, hybridizing the component device to the host substrate, andbonding the device to the host substrate.
 2. The method of claim 1,wherein the host substrate is selected from the group consisting ofglass, silicon, metals, and Langmuir-Blodgett films.
 3. The method ofclaim 1, wherein the step of preparing the host substrate for attachmentof DNA polymers includes the step of derivatizing the host substrateprior to attaching the DNA polymers.
 4. The method of claim 1, whereinthe step of hybridizing the component device to the host substrateincludes a conventional hybridization.
 5. The method of claim 1, whereinthe step of hybridizing the component device to the host substrateincludes an active hybridization using an electric field.
 6. The methodof claim 1, wherein the step of patterning the host substrate furtherincludes the step of selectively subjecting the host substrate to UVradiation.
 7. The method of claim 1, wherein the bonding step causes anelectrical contact between the host substrate and the device.
 8. Themethod of claim 7, wherein in the bonding step forms a metallurgicalbond between the host substrate and the device.
 9. The method of claim8, wherein the metallurgical bond is a metal bump.
 10. The method ofclaim 1, wherein the DNA polymers are modified DNA polymers.
 11. Themethod of claim 1, wherein the component device is a photonic device.12. The method of claim 10, wherein the photonic device is a lightemitting diode.
 13. The method of claim 10, wherein the photonic deviceis a photonic crystal.
 14. The method of claim 1, wherein the componentdevice is a micromechanical device.
 15. The method of claim 1 furtherincluding the step of transporting the component device to the hostsubstrate via application of an electronic force.
 16. The method ofclaim 15, wherein the electronic force is electroosmosis.
 17. The methodof claim 15, wherein the electronic force is electrophoresis.
 18. TheMethod of claim 15, wherein the electronic force is dielectrophoresis.19. The method of claim 15, wherein the electronic force is acombination of electroosmosis and electrophoresis.
 20. The method ofclaim 1, wherein the binding step includes a solder reflow process.